One of the biggest prisoner swaps since the cold war unfolded on the tarmac of Vienna's airport on Friday as two airplanes -- one carrying 10 accused Russian sleeper agents and the other with four Russians deemed to be spies for the West -- traded their human cargoes and took off into the bright clear sky.

An American official confirmed the exchange had taken place, hours after the 10 accused Russian spies were whisked out of the United States on a charter plane. The American and Russian airplanes landed and departed in what appeared to be a clockwork operation on a remote part of the runway in Vienna, once a hub of clandestine East-West maneuvering.

The exchange was part of a deal with Moscow to put a quick end to an episode that threatened to disrupt relations between the two countries.